1. Field of the Invention
The present invention relates to a heat-resistant member having a ceramic coating layer and a method for evaluating quality of a heat-resistant member.
2. Description of Related Art
A combustor, a nozzle, a blade, and the like forming a heat engine such as a jet engine, a gas turbine, or the like are used in a severe environment in which a high temperature and stress are applied to them. Up to now, therefore, a heat-resistant member made of a heat-resistant alloy has been used as a material for these machines.
In recent years, however, as a demand for making higher the temperature at which such machines as described above are used has become great in order to more effectively utilize energy resources, a heat-resistant member to be used in them has been required to be more greatly improved in heat resistance.
Thereupon, in order to meet such a demand, a heat-resistant member composed of a metallic substrate coated with a ceramic material which is small in thermal conductivity as a heat isolation layer has begun to be used.
Up to now, as a ceramic material of this kind, zirconia, for example, Y.sub.2 O.sub.3 -stabilized zirconia, CaO-stabilized zirconia, MgO-stabilized zirconia, and CaSiO.sub.3 and the like have been proposed and among them the stabilized zirconia, which is small in thermal conductivity and large in thermal expansion coefficient, is commonly used. The reason why a ceramic material having a large thermal expansion coefficient is used is that it is well matched with a metallic substrate.
As a means for coating such a ceramic material on a metallic substrate, a thermal spraying method is generally used for economic reasons.
However, in such a heat-resistant member having an existing ceramic coating layer, there has been a problem that spalling or delamination is induced in the ceramic coating layer while it is used for a long period of time and its original excellent heat resistance cannot be kept. It is thought that this is caused mainly by a thermal stress generated in the ceramic coating layer by difference of thermal expansion coefficience between a ceramic layer and a metal member.
And up to now, a standard for evaluating a ceramic coating layer in nondestructive method to predict its performance or properties has not been established and therefore, there has been also a problem that it is difficult to form in good repeatability a ceramic coating layer which is excellent in property making it possible to keep its heat resistance for a long time.